A person is a heterosexual because of the presence of genitalia of one sex or the other. No one except a very few with an exceedingly rare congenital deformity have both kinds of genitalia.
The term, “sexual orientation” is based entirely upon “feelings” according to the American Psychological Association definition. I went to great lengths with multiple examples and illustrations to point out that “feelings” do not “control” behavior. I also went to similar lengths to point out that descriptors based upon behavior do not apply to those who may “feel,” be “oriented,” a certain way but do not engage the behavior of the applicable descriptor.
Given that everyone born without the previously mentioned birth defect is heterosexual, the defining characteristic of homosexuality (not sexual orientation) is behavior. Behavior is a choice, as I am sure you agree. Therefore, one chooses to engage in homosexual behavior or not. if one chooses not to engage in homosexual behavior, then the descriptor of that behavior is not applicable regardless how that person may “feel” or be “oriented.”